Issues in Linking ATM networks via Satellite

This page lists some of the issues which need to be considered when transporting an ATM cell stream using a satellite link.

Which cell transport method should be used?

Various schemes are possible. Most demonstrator networks have chosen to use terrestrial frame formats (e.g. PLCP). These may be poorly suited to the satellite user needs.

Some of the poposed schemes include:

How does noise effect the cell stream?

satellite links typically offer lower rate connections than tereestrial systems, and although they may provide a reasonably low BER during normal operation, are subject to effects whihc produce occasional reduction in the link quality of service. These may lead to a loss of signal (outage) or prolonged burst of errors.

Some of the areas which need further investigation include:

How do corrupted cells effect the user?

The ATM cell layer provides only limited guarentees on the cell header (suing an 8-bit HEC) and no protection on the cell payload. This requires either an error-free channel or an application which is insensitive to errors. In practice, AAL-5 may be used to layer a packet-oriented service over the basic cell-service. This should provide full error detection.

Some of the issues include:

How does delay effect the user?

Satellite delay will be an issue for many services.

Some of the issues include:

How is the satellite bandwidth to be managed?

Many tests are being considered with fixed SCPC assigned circuits. These tests address the needs of the ATM applications but may not necessarily be representative of a future network of users who need to share the satellite capacity. Given the high data rates needed for many services, a dynamic assignment scheme seems very desirable in a "production system".

Some of the issues include:

How will applications perform?

Some of the types of applications which require study include:

Gorry Fairhurst - ERG home page